Outstanding Exposure - Components of BIG Net Par Outstanding (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Schedule of Insured Financial Obligations [Line Items]
Net	$ 236,383	$ 233,258
Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	226,746	224,099
Other structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	7,727	7,203
Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	9,637	9,159
BIG
Schedule of Insured Financial Obligations [Line Items]
Net	5,882	5,892
BIG | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	4,794	4,777
BIG | Other structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	100	105
BIG | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	1,088	1,115
BIG | BIG 1
Schedule of Insured Financial Obligations [Line Items]
Net	3,376	3,363
BIG | BIG 1 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	3,364	3,345
BIG | BIG 1 | Other structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	0	0
BIG | BIG 1 | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	12	18
BIG | BIG 2
Schedule of Insured Financial Obligations [Line Items]
Net	180	181
BIG | BIG 2 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	109	108
BIG | BIG 2 | Other structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	32	34
BIG | BIG 2 | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	71	73
BIG | BIG 3
Schedule of Insured Financial Obligations [Line Items]
Net	2,326	2,348
BIG | BIG 3 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	1,321	1,324
BIG | BIG 3 | Other structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	68	71
BIG | BIG 3 | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	1,005	1,024
United States | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	180,837	179,636
United States | RMBS
Schedule of Insured Financial Obligations [Line Items]
Net	1,910	1,956
United States | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	8,660	8,228
United States | BIG | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	3,804	3,796
United States | BIG | RMBS
Schedule of Insured Financial Obligations [Line Items]
Net	988	1,010
United States | BIG | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	1,088	1,115
United States | BIG | BIG 1 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	2,374	2,364
United States | BIG | BIG 1 | RMBS
Schedule of Insured Financial Obligations [Line Items]
Net	12	18
United States | BIG | BIG 2 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	109	108
United States | BIG | BIG 2 | RMBS
Schedule of Insured Financial Obligations [Line Items]
Net	39	39
United States | BIG | BIG 3 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	1,321	1,324
United States | BIG | BIG 3 | RMBS
Schedule of Insured Financial Obligations [Line Items]
Net	937	953
Non-U.S. public finance | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	45,909	44,463
Non-U.S. public finance | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	977	931
Non-U.S. public finance | BIG | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	990	981
Non-U.S. public finance | BIG | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	0	0
Non-U.S. public finance | BIG | BIG 1 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	990	981
Non-U.S. public finance | BIG | BIG 2 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	0	0
Non-U.S. public finance | BIG | BIG 3 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 0	$ 0